The long-term goals of this project are to provide detailed insight into the biosynthesis of 9-cis--retinoic acid (9cRA) at the nutritional, biochemical and molecular levels. The endogenous retinoid 9cRA serves as an activator of the ligand-dependent transcription facts RXRs. The three RXRs (Alpha, Beta, gamma) comprise a sub family of the steroid/thyroid/retinoid/vitamin D superfamily of hormone receptors. RXRs regulate development and growth by modulating expression of genes with TXT response elements and by heterodimerizing with and regulating the effects of several other receptors in the superfamily, such as the peroxisome proliferator activated receptors and the retinoic acid receptors, RARs. Yet little is understood concerning the biosynthesis of 9cRA. Thus, the immediate goals of the work proposed here are to expand our initial insight into the generation 9cRA. We hypothesize: 1) that a quantitatively important route physiologically of 9cRA biosynthesis involves conversion of 9-cis-retinol into 9-cis-retinal catalyzed by a short chain dehydrogenases, followed by conversion of 9-cis-retinal into 9cRA; and 2) therefore 9cRA biosynthesis may be regulated independently of all-trans-retinoic acid biosynthesis, i.e. all- trans-retinoic acid would not serve as an obligatory precursor of 9cRA. The specific aims are to: 1) determine whether the mitochondria and lamda subcellular fractions produce 9cRA from 9-cis- retinol, all-trans-retinol or all-trans retinoic acid; 2) clone the cDNA encoding a putative soluble 9-cis-retinol dehydrogenase kinetically and biochemically, including establishing the effects of vitamin A status on their expression and activities; and 4) determine which cells express 9-cis-retinol dehydrogenase(s) in embryos and adults by in situ hybridization. The cumulative data anticipated will contribute to establishing the pathways of 9cRA biosynthesis and provide insight into their regulation. These results also will contribute into regulation of RXT function and will provide reagents for future examination of pathology possibly associated with impaired 9cRA biosynthesis.